Kim Jong-un watches soldiers of the Korean People's Army taking part in drills. Photo: AFP

"Under the situation where a war may break out any moment, there is no need to keep up North-South military communications," the official told a South Korean counterpart before the hotline was disconnected.

He said the link would remain severed as long as the South's "anachronistic hostile acts continue".

Several weeks ago North Korea severed the Red Cross hotline used by the two governments to communicate in the absence of diplomatic relations.

The hotline mentioned on Wednesday is important because the Koreas use it to communicate as hundreds of workers travel back and forth to the Kaesong industrial complex. Officials say more than 900 South Korean workers were in Kaesong on Wednesday.

It also comes a day after North Korea's military put its "strategic" rocket units on a war footing, with a fresh threat to strike targets on the US mainland, Hawaii and Guam, as well as South Korea.

North Korea is angry over routine US-South Korean drills and recent UN sanctions punishing it for its February 12 nuclear test.